Household water softeners of the “ion exchange” type typically include a resin tank through which hard water passes to exchange its “hard” ions of calcium and magnesium for “soft” sodium or potassium ions from the resin bed. Regeneration of the resin bed is periodically required to remove the accumulation of hard ions and replenish the supply of soft ions. Regeneration is effected by flushing a solution of salt, i.e., a brine solution through the resin bed.
A separate brine tank is conventionally used to form the brine solution for use during the regeneration cycle. When regeneration is initiated in the softener system, the brine solution drawn from the brine tank passes through the bed of ion exchange material in the softener tank to reverse the exchange of ions and revitalize the bed by removing hardness inducing ions and replacing them with sodium or potassium ions from the brine. The regeneration cycle typically lasts about an hour and needs to be done, on average, about three or four times each week. More frequent regenerations are required in periods of greater than normal water usage. No regeneration is required when water usage ceases as typically happens when the occupants of a household go on a holiday or vacation. The cost of operating a water softener system may be reduced by limiting the amount of salt utilized in each regeneration cycle and the frequency of regeneration cycles to only that necessary to regenerate resin particles. Consequently, it is preferred that the brine solution have a concentration near its saturation point to minimize the amounts used for each regeneration cycle. Saturated solutions are less desirable since the salt in these solutions have a tendency to crystallize.
Most present day water softeners use a single resin tank for softening and are provided with automatic controls to regenerate the softening tank at periodic intervals. A drum containing a brine solution is typically connected to the resin tank and includes a concentrated aqueous solution of sodium chloride or potassium chloride. As previously discussed, the concentration of sodium chloride or potassium chloride is below the saturation point for the solution. However, the solubility characteristics for sodium chloride and potassium chloride are significantly different.
One problem addressed by the present invention is the difference in solubility behavior between various salts used as softeners, e.g., potassium chloride and sodium chloride. Sodium chloride solubility is less sensitive to temperature fluctuations than potassium chloride solubility. For example, at 0° C. the solubility of sodium chloride in water is about 35.7 grams per cubic centimeter (g/cc) of saturated solution whereas potassium chloride is about 27.6 g/cc. Increasing the temperature to 10° C. increases the solubility of a saturated sodium chloride solution to 35.8 g/cc and a saturated potassium chloride solution to 31.0 g/cc. Further incremental increases to 20° C. and 30° C. increase solubility of a saturated sodium chloride solution to 36.0 g/cc and 36.3 g/cc, respectively, whereas the solubility of a saturated potassium chloride solution increases to 34.0 g/cc and 37.0 g/cc, respectively. Clearly, the solubility of sodium chloride solutions are less sensitive to temperature fluctuations. Conversely, the solubility of potassium chloride solutions at different temperatures varies greatly.
It is important to note that water softener systems are not always operated in controlled environments. The temperatures that household water softeners are exposed can vary significantly. The changes in temperature fluctuations can have a catastrophic effect on potassium chloride brine solutions. Since, it is desirable to have highly concentrated brine solutions below the saturation levels, the changes from higher to lower temperatures can cause re-crystallization of the dissolved potassium chloride. Once initial re-crystallization occurs, crystallization continues and tends to displace the brining solution. As a result, the remaining brine solution cannot be drawn into the resin beds for regeneration of the resin beds causing system failure.
The present invention addresses this problem and provides for a process and apparatus for reducing the formation of salt crystals in the brine solution.